Figure 6.

Hypothetical fronto-basal-ganglia circuits for global and selective stopping. A. When the subject's hand is at rest, the GPi is tonically inhibiting thalamocortical output to hand representations so that these are only weakly active (small filled circles). By contrast, one M1 representation, for example for the speech system, is strongly active (large yellow-filled circle). B. The subject initiates a hand movement using the direct pathway. The PMC activates the putamen, the putamen inhibits the GPi, this removes inhibition from the thalamus and increases drive to the hand area of M1. C. The IFC sends input to the STN via the hyperdirect pathway. The STN has a broad effect on GPi, leading to global suppression of thalamocortical programs, including hand and speech systems. D. Proactive selective control may be set up via the indirect pathway. The DLPFC activates a specific channel of the caudate, the caudate inhibits a specific channel of the GPe, the GPe inhibits a specific channel of the GPi (directly or via the STN) and inhibition of a particular thalamocortical channel is prepared (but perhaps not triggered until stopping is needed). E. Action initiation occurs as for B. above, except it occurs with the proactive selective control system activated. This could lead to slower response emission. F. The indirect pathway may be triggered by the IFC when a stop signal occurs. This leads to suppression of one, but not all, representations in M1. M1 = primary motor cortex; PMC = premotor cortex; DLPFC = dorsolateral prefrontal cortex; IFC = inferior frontal cortex; PUT = putamen; CAUD = caudate; GPi = globus pallidus pars interna; GPe = globus pallidus pars externa; STN = subthalamic nucleus; THAL = thalamus.